High pressure discharge lamp containing an inert gas,mercury,a halogen and tin

ABSTRACT

In a high pressure discharge lamp including a luminous sealed tube containing an ionizable inert gas, mercury, bromine, iodine, and tin, the improvement therein wherein said halogen and tin are sealed in said luminous sealed tube in such quantities that the ratio between the number of atoms of the halogen and the tin is from about 1 for the halogen to between about 0.51 to about 3.0 for the tin and the ratio between the number of atoms of the bromine and the iodine is between 1:0.1 and 1:5.0.

United States Patent [72] Inventors LeoMori Tokyo; Tadatoshi I-Iigashi;Satoshi Nagano, Kawasaki-shi; Kiyoshi Saita, Yokosuka-shi,

Continuation of application Ser. No. 567,281, July 22, 1966, nowabandoned.

[54] HIGH PRESSURE DISCHARGE LAMP CONTAINING AN INERT GAS, MERCURY,I-IALOGENS AND TIN 4 Claims, 2 Drawing Figs.

[52] US. Cl. 313/229,

3,279,877 10/1966 Smithetal [51] Int. Cl HOlj 61/18 [50] Field ofSearch313/223, 224, 225, 226, 227, 228, 229

[5 6] References Cited UNITED STATES PATENTS Primary Examiner-Raymond F.Hossfeld Attorney-George B. Oujevolk ABSTRACT: In a high pressuredischarge lamp including a luminous sealed tube containing an ionizableinert gas, mercury,

'bromine, iodine, and tin, the improvement therein wherein said halogenand tin are sealed in said luminous sealed tube in such quantities thatthe ratio between the number of atoms of the halogen and the tin is fromabout 1 for the halogen to between about 0.51 to about 3.0 for the tinand the ratio between the number of atoms of the bromine and the iodineis between 1:0.1 and 1:5.0.

HIGH PRESSURE DISCHARGE LAMP CONTAINING AN INERT GAS, MERCURY HALOGENSAND TIN This application is a continuation of US. Pat. application No.567,281 filed Jul. 22, 1966 (now abandoned).

The present invention relates to electric discharge lamps and moreparticularly to an electric discharge lamp for illumination purposeshaving a continuous spectrum over a wide range of wavelength, thusexhibiting uniform and good color rendering property.

Discharge lamps commonly available on the market, for example, ahigh-pressure mercury arcdischarge lamp comprises a discharge tube orsealed tube which is made of fused quartz and contains argon gas sealedtherein at a pressure of several millimeters Hg and mercury of aquantity of several milligrams per cubic centimeter of the inner volumeof the sealed tube and an evacuated envelope containing said sealedtube. However, the conventional mercury arc discharge lamp is notsuitable for general purpose illumination because the spectrum radiatedby mercury atoms contains a large amount of light of shorter wavelengthbut less amount of light of longer wavelength in the visible range sothat .their color-rendering property is poor.

It is known that the color-rendering property of such mercury dischargelamps can be improved by utilizing halides of metals e.g. halides ofelements of group Ia of the periodic table such as sodium iodide andlithium iodide, halides of elements of group lllb such as thalliumiodide and indium iodide, or halides of lanthanide elements or actinideelements or elements of group llla, such as thorium iodide and scandiumiodide together with mercury. Each of these halides has a sufficientvapor pressure at the wall temperature of the sealed tube duringoperation and undergoes dissociation at the temperature of an arc columnbetween electrodes to form metal atoms and halogen atoms and thedischarge spectrum of these free atoms is included in the visible range.Accordingly when an electric discharge is created across a pair ofelectrodes disposed in the sealed tube of the electric discharge lamp,metal halides contained in the tube will be vaporized and dissociated bythe temperature rise of the tube wall caused by the heat of electricarc. Thus, line spectra which are characteristic of respective metalatoms are radiated to improve the color rendering property of thedischarge lamp. It is also well known in the art that thecolor-rendering property can be further improved by utilizing severalmetal halides of different type.

With only one type of metal halide the spectral distribution in thevisible range is not uniform so that the color and colorrenderingproperty is not satisfactory for use as a source of illumination forgeneral purposes. Even when several types of metal halides are mixed forthe purpose of producing more uniform spectral distribution as abovementioned it would also be difficult to obtain satisfactorycolor-rendering property because of the limitation upon spectral linesof metal caused by electric discharge. Moreover, utilization of a numberof types of compounds results in the increase in the chance ofcontamination by impurities which greatly affects the life of thedischarge lamp.

It is an object of this invention to provide a novel electric dischargelamp comprising a sealed tube in which mercury, an ionizable inert gas,halogen and tin are sealed whereby to enable to emit light rays having aspectral energy distribution which is continuous over the visible range,said discharge lamp being also characterized by having an improvedcolor-rendering property, high efficiency, as well as improved qualityand operating life.

A further object of this invention is to provide an improved electricdischarge lamp wherein halogen and tin which are sealed in the tube issealed such that the ratio between the number of atoms of the halogenand the tin is 1 0.51 and l 3.0 whereby to prevent discharge initiatingvoltage from increasing during repeated turn on and off operations ofthe lamp.

A still further object of this invention is to utilize both bromine andiodine as halogen in the electric discharge lamp herein disclosed withthe ratio of the total atom number of from 1 0.1 to l 5 whereby toprovide discharge lamps with very small decrease in the luminous fluxemitted therefrom during continuous operation over a long period oftime.

Further objects and advantages of the present invention will becomeapparent and this invention will be better understood from the followingdescription, reference being made to the accompanying drawings, inwhich:

FlG. l is an elevation of an electric discharge lamp embodying thisinvention; and

FIG. 2 is a graph showing the relative spectral energy distribution oflight rays emitted from an electric discharge lamp embodying thisinvention.

Referring now to the accompanying drawings. in FIG. I is shown anelectric discharge lamp comprising an evacuated envelope 1 made oftransparent glass having a base 2 at one end thereof. A supporting frame3 made of metal wire is disposed within the envelope adapted to supporta luminous sealed tube 4. The sealed tube 4 is made of a transparentfused quartz glass tube with its opposite ends pressed. Within the glasstube 4 are disposed a main electrode 6 at one end, and another mainelectrode 9 and an auxiliary electrode 10, at the opposite end, whichare respectively supported by lead-in .conductors 5, 7 and 8 sealed insaid pressed portions. The main electrode 6 is electrically connected toone terminal of the base via the supporting frame 3, and a lead-inconductor 12 which is sealed in a stem 11, while the other mainelectrode 9 is connected to the other terminal of the base via a lead-inwire 13 similarly sealed in the stem 11. The auxiliary electrode 10 isconnected to the supporting frame 3 through a starting resistor. 15. Inthe sealed tube 4 are sealed an ionizable inert starting gas such asargon at a pressure of 10 to 40mm. Hg, mercury ofthe quantity of 0.8 to6mg. per cubic centimeter of the inner volume of the sealed tube and tinhalides.

When impressed with a starting voltage from a conventional startingdevice, the electric discharge lamp constructed as above described willinitiate a glow discharge between the main electrode 9 and the auxiliaryelectrode 10 followed by an arc discharge between the main electrodes 9and 6. The heat generated by this discharge will heat the sealed tube 4,thus increasing the vapor pressure of mercury and tin halides which arecontained therein. The vaporized tin halides emit a strong continuousspectrum in the visible range, while at the same time the vaporizedmercury and the vapor of dissociated tin emit line spectrum composed of405g, 436p. and 578 mercury lines and 453p. and 563p. tin lines. In thisway tin halides utilized according to this invention will act tocomplement the light in the wavelength region in the spectrum which isnot atforded by mercury, with the result that the spectral energydistribution is made more uniform'and the color-rendering property isimproved. i

The tin halides sealed in the sealed tube may be applied in the form ofeither elementary substances or their compounds. Among such compoundsmay be mentioned stannous iodide, stannic iodide, stannous bromide,stannic bromide and the like. Further, mercury halide may be usedtogether with tin in the form of elementary substance.

Where tin is utilized in the form of halides, the adequate quantity oftin element is within a range of from 0.01 to 2mg. per cubic centimeterof the inner volume of the sealed tube. Within this range thecolor-rendering property could be effectively improved and there is nofear that, during operation of the lamp, tin halide is deposited on theinner wall of the sealed tube in the form of liquid or solid state. lfthe quantity of tin element exceeds 2mg. per cubic centimeter the arccolumn of the discharge become occasionally unstable.

When halogenand tin are used in such a quantity that the .ratio ofhalogen to tin (ratio of their number of atoms) is l 0.51 to 3.0 it ispossible not only to improve the color-rendering property but alsoeffectively prevent increase in the discharge initiation voltage at thetime of restarting the lamp after extinguishment. The ratio of halogento tin is selected so that the proportion of tin is higher than that ofthe case utilizing tin halide. Since tin is divalent or tetralavent, theratio of halogen and tin (the ratio of their number of atoms) of astable tin halide is 0.5 or 0.25. As a result, after the lamp is turnedoff, free halogen will not remain in the sealed tube thus the increasein the discharge initiation voltage is prevented. In this case the upperlimit of adequate quantityof tin element is mg. per cubic centimeter ofthe inner volume of the sealed tube.

Where a combination of bromine and iodine is selected as the halogen andwhere the ratio of the number of atoms of iodine to that of bromine isselected to be 0.1 to 5 l it is very effective to improve thecolor-rendering property and the efficiency of the discharge lamps inaddition to' preventing decrease in the luminous flux after long timecontinuous operation. Bromine and iodine in the range specified aboveserve to capture the tin which is sealed in together with them toprevent the tin from depositing on the inner wall of the sealed tubeunder operation, thus preventing the light transmitting property of thesealed tube from decreasing and prolonging the useful life of thedischarge lamps.

The following specific examples of this invention are given by way ofillustration, and are not to be construded as limiting in any way thescope and spirit of the invention.

EXAMPLE 1 mercury of the quantity of from 1 to 6mg. per cubic centimeterof the inner volume of the sealed tube and a quantity of stannous iodideof the amount corresponding to 0.2mg. of tin element per cubiccentimeter of the inner volume of the sealed tube. The following are theresults of experiments when this lamp was operated at an input power of400W.

1. Spectral Energy Distribution The spectral energy distribution oflight rays emitted from said discharge lamp is plotted in FIG. 2. FIG. 2shows that the spectral energy distribution is made more uniform overthe entire visible range by the reasons that by superposing light raysof wavelengths of 405p, 436g, 546p, and 578a corresponding to the linesof mercury upon light rays of wavelengths of 453 u and 563p.corresponding to the resonance lines of tin and that these superposedlight rays cooperate with a continuous spectrum having its maximumwavelength near about 650;; to provide nearly uniform spectral energydistribution over the entire visible range.

2. Chromaticity It was found that the chromaticity was very close to thelocus of a black body at a color temperature of about 4,200l(. Otherexperiments showed that by varying the quantity of incorporation ofstannous iodide white light which is nearly ideal as the light source ofillumination was obtained having chromaticity close to the locus of ablack body at a color temperature in a range of about 6,000K. to 4,000K.

3. Color-rendering Property Color-rendering indices calculated from thespectral energy distribution curve shown in FIG. 2 by a test colormethod as specified by the Commission Internationale de lEclairage (C.l. E.) showed the general color-rendering index Ra 86 and a specialcolor-rendering index for red color R 75. These values are comparablewith those of the most excellent fluorescent lamps of deluxe color type.

4. Efficiency 1 I The efficiency of the lamp was found to beapproximately 50 lumens per watt. This value is comparable with that ofconventional mercury discharge lamp with or without phosphorous. Whileit has been well known in the art that special mercury lampsincorporated with thallium iodide and sodium iodide often exhibit anefficiency of approximately 80 lumens per watt, it is not proper tocompare the novel lamp with such lamps because their color-renderingproperty and chromaticity are very poor.

5. Performance Since stannous iodide contained in the sealed tube andelementary substances dissociated therefrom by the action of electricdischarge are all chemically stable, the lumen maintenance and lifecharacteristic of the discharge lamps embodying this invention aresuperior to those of discharge lamps containing sodium iodide or indiumiodide.

6. Flickering of Light Output In this example, although the dischargelamp was energized from an AC source, flickering of light output wasvery slight. This is because in the discharge lamp of this invention,fluctuation in the continuous spectrum in which light rays are emittedat a relatively low temperature ranges of from 20 to 30 percent and suchlight rays comprise the major portion of the light output.

EXAMPLE 2 An electric discharge lamp was prepared by sealing a mixturein a sealed tube made of quartz glass, having a diameter of 18mm. and aspacing between discharge electrodes of 65mm, said mixture consisting ofargon gas at a pressure of 20mm. Hg, 40mg. of mercury, 16mg. of stannousbromide and 5mg. of metallic tin (the ratio between the numbers ofbromine atom and tin atom being approximately 1 1). This discharge lampreadily started at a discharge initiating voltage of from 300. to 400.,and it was noted that there was no appreciable rise in the dischargeinitiating voltage after repeating turning on and off operations manytimes. The spectral energy distribution of light rays emitted fromthislamp was a uniform spectrum consisting of a major continuousspectrum having its maximum wavelength near 500p. and line spectrum ofmercury having wavelengths of 405;/., 436 1., 546p. and 57811. and linespectrum of tin having wavelengths of 452p. and 563 which are superposedupon said continuous spectrum portion. C olor-rendering indicescalculated from this spectrum energy distribution curve by using thetest color methodspecified by the Commission Internationale deIEclairage were the general color-rendering index Ra 94 and the specialcolor-rendering index for red R 75. These ,values are comparable withthose of especially high quality fluorescent lamps of super deluxe type.The efficiency of the discharge lamp of this example was found to beabout 60 to 65 lumens per watt which is higher than the conventionalmercury mercury lamps with or without phosphorous.

EXAMPLE 3 Another electric discharge lamp was prepared by sealing amixture in a sealed tube made of quartz glass and having a diameter of18mm, and a spacing of 65mm. between discharge electrodes, said mixtureconsisting of argon gas at a pressure of 25mm. Hg, 40mg. of mercury,10mg. of stannous bromide and 8mg. of stannous iodide (the ratio of atomnumbers of bromine and iodine being about 1 to 0.6). After .continuousoperation of 1,000 hours at an input of 400 watts no metallic depositwas noted on the inner wall of the sealed tube thus the lamp radiated 95to. 98 percent of the initial light fluxes. Further, no appreciable wearof discharge electrodes was not noted. The color-rendering indices ofthis lamp were high, that is, the general color-rendering index Ra 91and the special color-rendering to red color R 70. The efficiency ofthis lamp was about 65 lumens per watt.

We claim:

l. A high-pressure discharge lamp with enhanced color rendition and freeof internal metal deposition during the service life of the lamp,including a luminous sealed tube'containing a pair of dischargeelectrodes an ionizable inert gas, mercury, tin, bromine, and iodine,the relative proportions of bromine and iodine being such that the ratiobetween the number of atoms of the bromine and the iodine is between 10.1 and l 5.0 to prevent metal deposition on the inner wall of saidsealed tube and wear of said discharge electrodes.

2. A high-pressure discharge lamp according to claim ll wherein theamount of tin contained in said luminous sealed 6 tube is between about0.01 mg. and about 2 mg. per cubic cen- 4. A highpressure discharge lampaccording to claim 3 "meter of the volume of Said luminous sealedwherein the amount of tin contained in said luminous sealed 3. Ahigh-pressure discharge lamp according to claim 1 wherein the ratio ofthe number of atoms of bromine and iodine to the number of atoms of tinis between 1 0.51 and 1 5 tube is between about 0.01 mg. and about mg.per cubic centimeter of the inner volume of said luminous sealed tube.

2. A high-pressure discharge lamp according to claim 1 wherein theamount of tin contained in said luminous sealed tube is between about0.01 mg. and about 2 mg. per cubic centimeter of the inner volume ofsaid luminous sealed tube.
 3. A high-pressure discharge lamp accordingto claim 1 wherein the ratio of the number of atoms of bromine andiodine to the number of atoms of tin is between 1 : 0.51 and 1 : 3.0. 4.A high-pressure discharge lamp according to claim 3 wherein the amountof tin contained in said luminous sealed tube is between about 0.01 m.g.and about 10 mg. per cubic centimeter of the inner volume of saidluminous sealed tube.